CN101335308A

CN101335308A - Ultraviolet detector having internal gain and preparing method

Info

Publication number: CN101335308A
Application number: CNA2008100411592A
Authority: CN
Inventors: 王玲; 许金通; 袁永刚; 包西昌; 张文静; 李超; 张燕; 李向阳
Original assignee: Shanghai Institute of Technical Physics of CAS
Current assignee: Shanghai Institute of Technical Physics of CAS
Priority date: 2008-07-30
Filing date: 2008-07-30
Publication date: 2008-12-31
Anticipated expiration: 2028-07-30
Also published as: CN101335308B

Abstract

The invention discloses an ultraviolet detector with internal gain and a preparation method thereof which reduces the dark current under large reversed bias voltage through a plurality of times of surface treatment and double passivation so as to promote the performance of the device under the large reversed bias voltage. The detector obtained by utilizing the method has stable internal gain and can realize the purposes that detected signals are magnified in the detector and the signal-to-noise ratio of the whole testing system is relatively improved. The detector related by the invention has p-i-n structure; the preparation method thereof comprises mesa etching, electrode growing, and passivation layer preparing, etc. Compared with the common GaN-based ultraviolet detector, the ultraviolet detector provided by the invention has the advantages of having internal gain, small dark current, stable performance, simple preparation technology, high signal-to-noise ratio of detection, and can detect weak ultraviolet signals, etc.

Description

A kind of ultraviolet detector and preparation method with interior gain

Technical field

Photodetector that the present invention relates to and manufacturing process technology specifically are meant the visible blind ultraviolet detector and the technology of preparing that gain in having.

Background technology

Nowadays, the ultraviolet detection technology has more and more demonstrated its importance, and small-signal is surveyed detector performance is had higher requirement.The ultraviolet detector of gain in once ultraviolet vacuum tube of Chu Xianing and Si base, SiC base etc. had, the drawbacks limit that self is intrinsic they in the application prospect in ultraviolet detection field, and the GaN base semiconductor ultraviolet detector that is operated in gain in the having of ultraviolet band can overcome the deficiency of these aspects just.Such detector all has very application prospects in every field such as laser imaging radar, environment detection, fluorescence, long-range detections, the distance that both can obtain moving target by detectable signal also can be known the translational speed of target, therefore can accurately survey moving target, this be conventional detector the work that can't finish.The interior gain of the mentioned detector of the present invention is quickened by anti-electric field partially in the i layer by photo-generated carrier and with material atomic collision its generation electron-hole pair is obtained.In view of the restriction of GaN material growing technology aspect, the device architecture of development mainly is Schottky (Schottky) structure, p-i-n structure etc. at present.The light signal that is detected also can advance detector and affact intrinsic (i) type GaN layer from p type GaN material layer direction incident (just according to formula) from substrate direction incident (back-illuminated type), and it is that electronics or hole cause ionization by collision and obtain interior gain that different incident modes corresponds respectively to.At the detector of gain back-illuminated type p-i-n structure in having, mainly be to realize in the world at present by the thickness that reduces n type GaN.But the thickness of the n section bar bed of material is more little, the series resistance of the device for preparing is big more, make its anti-inclined to one side dark current big more, the slope of straight line portion will be healed greatly accordingly on the multiplication characteristic curve, is an adverse factors for the device that is operated under the Geiger mode angular position digitizer (Geiger).Simultaneously, take into account the restricting relation between material growing technology, device preparation technology and the device performance three, make that the photosurface area of device can not too greatly can not be too little, have the photosurface diameter of the device of report mainly to concentrate between 30 microns to 50 microns at present.The anti-dark current partially of managing to reduce device in addition also is a technical barrier, performances such as the multiplication of the photoelectric device of gain, noise in influence has.

Summary of the invention

The purpose of this invention is to provide a kind of ultraviolet detector and preparation method thereof, solve the difficult problem in existing ultraviolet detection technology and the device preparation process, improve detectivity weak ultra-violet radiation signal with interior gain.

The UV photodetector with interior gain that the present invention narrated is pin ⁺Structure, epitaxial material has five-layer structure shown in Figure of description 1, at first epitaxial growth AlN (high and low temperature growth) or GaN resilient coating 2 on sapphire, Si or the SiC substrate 1 of two throwings, buffer layer thickness is generally 0.5um-3um, reduces the density of defects that causes because of lattice mismatch in the epitaxial material as far as possible.Then be three layers of epitaxial material: n-Al _xGa _1-xN:Si (0＜x＜1) layer 3, its thickness and doping content are respectively 0.1um～0.3um and 10 ¹⁶～10 ¹⁸/ cm ³I-GaN (mix) layer 4 its thickness and carrier concentration are respectively 0.1um～0.6um and～10 ¹⁵/ cm ³P-GaN:Mg layer 5, its thickness and doping content are respectively 0.5um～1um and 10 ¹⁸～10 ¹⁹/ cm ³The light signal of incident is quickened by the internal electric field of i layer at the photo-generated carrier (electronics or hole) of p layer (just according to formula) and i layer (by shining formula) generation, after obtaining sufficiently high energy, obtain electron-hole pair with basis material atomic collision, newborn electronics or hole produce new electron-hole pair because of quickening collision again, just can obtain the multiplication of photoelectric current according to the method, realize the interior gain of detector.The structure of the ultraviolet detector that on epitaxial material, prepares such as accompanying

drawing

2 and 3, the Ni/Au/Ni/Au of p type contact electrode 6 electron beam evaporation deposits; Ground floor passivation layer 7 is the SiO that utilize the PECVD technology growth ₂Or Si ₃N ₄, n type contact electrode 8 is the Ti/Al/Ti/Au of electron beam evaporation deposit; Second layer passivation layer 9 is the SiO that utilize the PECVD technology growth ₂Or Si ₃N ₄The metal that adds thick electrode 10 and interconnecting electrode 11 deposits growth is Cr/Au.

Technology of preparing comprises the general technology for preparing conventional detector, is summarized as follows:

(1) ultrasonic wave organic solvent, plasma clean material surface.

(2) electron beam, evaporation deposition growing metal electrode and thickening and interconnecting electrode.

(3) ICP etching table top becomes knot.

(4) PECVD technology, magnetron sputtering technique growth of passivation layer.

But in view of the characteristics of the ultraviolet detector with interior gain that the present invention relates to, the special character on technology of preparing is as follows:

(1) the repeatedly surface treatment of etching table top: (20% (mass ratio) KOH aqueous solution is heated to boiling for nitrogen plasma treatment (processing time is about 20 minutes), the KOH aqueous solution, soak test material 15 seconds) and thermal annealing (temperature is 700 ℃ in nitrogen atmosphere, time is 1 minute), the sulfuration, according to these steps, can remove etch product, the etching injury on surface and the influence that lattice is caused, just can reduce to leak electricity and increase the electric property and the optical property of contact electrode.

(2) two passivation technologies carry out surface treatment behind the ICP etching table top, utilize the SiO of PECVD technology growth then ₂, thickness is 1500～2500 dusts, deposit growth Ti/Al/Ti/Au utilizes acetone treatment well later passivation layer and metal level to be carried out thermal annealing (time is 15 minutes, and temperature is 550 ℃) in nitrogen atmosphere then, utilizes PECVD technology growth SiO at last ₂Be second layer passivation layer, this layer passivation etching opened the size of electrode hole than for the first time little 20 microns, reduces as much as possible to leak electricity to the influence of device performance around extension electrode and the electrode.

(3) photo etched mask glue just can be alleviated the phenomenon that device photosurface area dwindles for thin glue for the first time.

Ultraviolet detector of the present invention is compared with the general ultraviolet detector, outstanding characteristics are to have interior gain, can the photogenerated current that detection obtains be exaggerated in detector inside, avoid of the influence of the noise of the reading circuit that links to each other with detector as much as possible to weak UV signal, thereby improve the signal to noise ratio of whole probe assembly, also can be used for accurately surveying, long-range detection etc.

Figure of description

Fig. 1 is the structural representation of epitaxial material;

Wherein 1 is the substrate of epitaxial material; 2 is AlN or GaN resilient coating; 3 is n type Al _xGa _1-xThe N material layer; 4 is i type GaN material layer (intrinsic material), and the zone of multiplication takes place photo-generated carrier; 5 is the p-GaN material layer.

Fig. 2 is the cross-sectional view of the device of gain in having;

Wherein 6 is the p contact electrode, and contacting metal is the Ni/Au/Ni/Au of electron beam evaporation deposit; 7 for utilizing the SiO of PECVD technology growth ₂Or Si ₃N ₄, be the ground floor passivation layer; 8 is n type contact electrode, and contacting metal is for being the Ti/Al/Ti/Au of electron beam evaporation deposit; 9 for utilizing the SiO of PECVD technology growth ₂Or Si ₃N ₄, be second layer passivation layer; 10 and 11 are respectively and add thick electrode and interconnecting electrode, and the metal of deposit growth is Cr/Au.

Fig. 3 is the vertical view of Fig. 2.

Fig. 4-Fig. 6 is a process chart.

Embodiment

Adopt the p-i-n of MOCVD technology growth below in conjunction with Figure of description ⁺The GaN sill of structure, the preparation technology of ultraviolet detector illustrates the preparation method with interior ultraviolet detector that gains that the present invention mentions:

1. select high-quality matrix epitaxial material according to the transmission spectrum and the XRD test result of material, require to see through district's internal transmission factor greater than 80% and have periodic vibration, the value of FWHM is as far as possible little.

2. chloroform, ether, acetone, ethanol ultrasonic cleaning epitaxial wafer, per step will clean about 5 minutes.

3. electron beam evaporation growth Ni/Au/Ni/Au, every layer thickness is 180～250 dusts

The growth electrode

Before with the mixed liquid dipping of ethanol and hydrochloric acid about 8～15 minutes, to remove the oxide on surface, with nitrogen plasma treatment sample is carried out surface clean again.

4. photoetching for the first time, photoresist used during photoetching is AZ-4260, gets rid of thin mask lithography glue, the time-temperature of preceding baking and back baking is respectively: 65 ℃ and 30 minutes.Utilize Ni, Au corrosive liquid to form circular p type contact electrode 6 after the photoetching.

Electron beam evaporation 1600～

The mask of Ni during as the ICP etching.

6.ICP be etched into table top, etching condition is: Ar/Cl ₂/ BCl ₃=3/3/24sccm, etching power are 350W, and bias voltage is 100V.Measure table surface height and be 5500～

7. nitrogen plasma treatment is after 20 minutes, and 10%～20%KOH (w.t.) solution is heated to boiling, and sample was soaked 10 seconds～20 seconds, carry out rapid thermal annealing then in nitrogen atmosphere, temperature is 700 degree, and the time is 1 minute, 30 minutes time is handled in last auto-vulcanization.

8. utilize PECVD growth regulation one deck SiO ₂Passivation layer 7, its thickness be 1500～

9. utilize photoresist to be corrosion and passivation layer SiO ₂Mask, to remove the surface of the sample of wanting deposit growth electrode, corrosive liquid is the HF buffer solution, corrosion is till expose material surface.

10. four layers of metal of electron beam evaporation growth Ti/Al/Ti/Au are as n type contact electrode, and the electrode after utilizing acetone to deposit is handled, and carries out rapid thermal annealing then in nitrogen atmosphere, to form n type Ohm contact electrode 8.

11. utilize the growth of PECVD method SiO ₂As second layer passivation layer 9.

12. the corrosion and passivation layer is opened electrode hole, method is with step 9.

13. electrode bundle sputter growth adds thick electrode 10 and welding interconnecting electrode 11, metal species Cr/Au.

Claims

1. one kind has the interior ultraviolet detector that gains, it by substrate (1), resilient coating (2), three layers of epitaxial material layer (3,4,5), P type contact electrode (6), n type contact electrode (8), first passivation layer (7), second passivation layer (9), add thick electrode (10) and interconnecting electrode (11) and constitute, it is characterized in that:

A. the material of substrate (1) employing is sapphire, Si or the SiC of twin polishing;

B. resilient coating (2) be substrate (1) go up by outside derive long aluminium nitride or gallium nitride buffer layer thin film, thickness is 0.5um to 3um;

C. epitaxial material layer (3) is n-Al _xGa _1-xN:Si (0＜x＜1), its thickness is 0.1um to 0.3um, doping content is 10 ¹⁶/ cm ³～10 ¹⁸/ cm ³

D. epitaxial material layer (4) is i-GaN, and its thickness is 0.1um to 0.6um, and carrier concentration is～10 ¹⁵/ cm ³

E. epitaxial material layer (5) is p-GaN:Mg, and its thickness is 0.5um to 1um, and doping content is 10 ¹⁸/ cm ³～10 ¹⁹/ cm ³

F. first passivation layer (7) and second passivation layer (9) are the SiO that utilizes the PECVD technology growth ₂Or Si ₃N, the thickness of first passivation layer (7) are 1500 dust to 2500 dusts, and the thickness of second passivation layer (9) is 800 dust to 1000 dusts;

G.P type contact electrode (6) is the Ni/Au/Ni/Au of electron beam evaporation deposit;

H.n type contact electrode (8) is the Ti/Al/Ti/Au of electron beam evaporation deposit;

I. adding thick electrode (10) and interconnecting electrode (11) is that the metal that deposit is grown is Cr/Au.

2. a kind of ultraviolet detector according to claim 1 with interior gain, it is characterized in that: after extension material layer (3,4,5) mesa etch operation was finished, little table top carried out surface treatment according to the following steps:

A. nitrogen plasma treatment, the processing time is about 20 minutes;

B. in the KOH aqueous solution of the mass ratio 10% to 20% that is heated to boiling, soaked for 15 seconds;

C. anneal in nitrogen atmosphere, temperature is 700 ℃, and the time is 1 minute;

D. vulcanizing treatment.